1. Field of the invention
This invention relates in general to wrenches, and in particular to a wrench having improved driving action.
2. Description of the Prior Art
In a conventional wrench, whether open end or adjustable, the jaws have parallel faces which slide over the sides of the nut. The faces are straight, flat surfaces.
A clearance is provided between the faces of the jaw and the nut. This clearance is necessary in order to be able to easily slide the jaw over the nut. Also, tolerances for manufacturing must be provided.
As a result, when the user applies torque, the jaw will first rotate a few degrees relative to the nut. This places the drive faces in contact with the corners of the nut. Basically, the drive will be on a single point contact on each jaw portion. Very little surface area of the sides of the nuts will be in contact with the jaw faces. As a result, if the nut is very tight, there is a tendency for the wrench to deform the metal of the nut, rounding the corners.
The drive point on one of the jaws will be close to the free end of the jaw because of the single point contact with the nut. This creates a long moment arm above the shank of the wrench. This long moment arm requires heavy jaw portions in order to prevent bending of the jaws under high torque.
Adjustable wrenches require that the user tighten the movable jaw on the nut each time the wrench is placed on the nut. Then, to remove the wrench at the end of a stroke, the user normally has to loosen the movable jaw. The user has to retighten the wrench at the beginning of the next stroke. Also, often the adjusting worm gear will tend to loosen as the wrench is used.
Adjustable open-end wrenches of traditional design are not recommended for driving in a reverse direction. This is the result of excessive stress being placed on the adjusting screw threads during reverse drive mode, causing warping and breaking of the adjusting screw.
In action, the nut acts as a rotating wedge between the upper and lower jaws of the wrench. The jaw spreading force thus imparted to the wrench finds the weakest part of this design, which is the adjusting screw which holds the movable lower jaw in position.
In forward driving direction, the jaw spreading force against the lower movable jaw is at the forward, lower nut corner. This force acts through a long moment arm. The force pivots the jaw slide rack on the adjusting screw threads and twists the jaw slide, partially locking it in its channel by drag force. Enough of the jaw spreading force is then carried by the wrench body in this way to permit safe forward drive without damage to the adjusting screw threads.
This is not so in reverse drive direction. In reverse drive, the jaw spreading force is exerted on the lower jaw at a point of rearward nut corner contact. The force is very close to and parallel to the jaw post as it tends to slide down and out of its channel. The force is at 90 degrees to the adjusting screw threads and the short moment arm through which it acts is insufficient to twist lock the jaw post in its channel. The result is that almost none of the nut imparted jaw spreading force is transmitted to the wrench body and must be borne by the adjusting screw threads.
The traditional method of dealing with this problem has been to attach the wrench handle at a 20 degree or more angle to the driven nut's centerline. This makes the flopping of this type wrench for 30 degrees drive stroke increments impossible and reverse driving of the nut impractical. Also, if attempted to be used for reverse drive, the force is still transmitted to the adjusting screw threads.